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Machine Guards and Safeguarding |
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Safeguards are essential for protecting workers from needless and
preventable injuries. Workers who operate and maintain machinery
suffer approximately 18,000 amputations, lacerations, crushing
injuries, abrasions, and more than 800 deaths per year, according to
OSHA, which rules that any machine part, function, or process that
may cause injury must be safeguarded. When the operation of a machine or accidental contact with it can injure the operator or others in the vicinity, the hazards must be either eliminated or controlled. Many hazards are created by moving machine parts. Safeguards are essential in such settings, and to ensure the safety of machine operators and other employees, safety managers should consider the following with regards to machine guarding. The purpose of machine guarding is to protect the machine operator and others in the work area from hazards created by ingoing nip points, rotating parts, flying chips and sparks. Some examples of this are barrier guards, light curtains, twohand operating devices, etc. Guards shall be affixed to the machine where possible and secured elsewhere if for any reason attachment to the machine is not possible. The guard shall be such that it does not offer an accident hazard in itself. Point of Operation Guarding The point of operation is the area on a machine where work is performed. Machines that expose an employee to injury must be guarded. The guarding device must be in conformity with appropriate standards. If specific standards are not available, the machine construction should prevent the operator from having any part of his body in the danger zone during the operating cycle. Special hand tools used for placing and removing material from point of operation areas must allow easy handling of the material without the operator in the danger zone. The following are some of the machines that usually require point of operation guarding: • Guillotine cutters; • Shears; • Alligator shears; • Power presses; • Milling machines; • Power saws; • Jointers; • Portable power tools; and • Forming rolls and calendars. If working with revolving barrels, containers and drums, guard by an enclosure interlocked with the drive mechanism, so the barrel, gun, or container cannot revolve unless the guard enclosure is in place. When the periphery of the blades of a fan is less than seven feet above the floor or working level, the blades must be guarded. The guard must not have openings larger than one-half inch. Safeguarding A safeguarding device may perform one of several functions. It may stop the device uses a radio beam that is part of the machine control circuit. When the capacitance field is broken, the machine will stop or will not activate. Like the photoelectric device, this device shall only be used on machines that can be stopped before the worker can reach the danger area. This requires the machine to have a friction clutch or other reliable means for stopping. Machine cycling will not start when the capacitance field is interrupted. When the capacitance field is disturbed by any part of the operator’s body during the cycling process, immediate machine breaking is activated. Electromechanical The electromechanical sensing device has a probe or contact bar that descends to a predetermined distance when the operator initiates the machine cycle. If there is an obstruction preventing it from descending its full predetermined distance, the control circuit does not actuate the machine cycle. The contact bar or probe travels a predetermined distance between the operator and the danger area. Interruption of this movement prevents the starting of machine cycle. Pullback Pullback devices utilize a series of cables attached to the operator’s hands, wrists, and/or arms. This type of device is primarily used on machines with stroking action. When the slide/ram is up between cycles, the operator is allowed access to the point of operation. When the slide/ram begins to cycle by starting its descent, a mechanical linkage automatically assures withdrawal of the hands from the point of operation. As the machine begins to cycle, the operator’s hands are pulled out of the danger area. Restraint The restraint (holdout) device utilizes cables or straps that are attached to the operator’s hands and a fixed point. The cables or straps must be adjusted to let the operator’s hands travel within a pre predetermined safe area. There is no extending or retracting action involved. Consequently, hand-feeding tools are often necessary if the operation involves placing material into the danger area. Trip Controls Safety trip controls provide a quick means for deactivating the machine in an emergency situation. A pressure-sensitive body bar, when depressed, will deactivate the machine. If the operator or anyone else trips, loses balance or is drawn toward the machine, applying pressure to the bar will stop the operation. The positioning of the bar, therefore, is critical. It must stop the machine before a part of the employee’s body reaches the danger area. Two-hand control The two-hand control requires constant, concurrent pressure by the operator to activate the machine. This kind of control requires a part-revolution clutch, brake, and a brake monitor if used on a power press. With this type of device, the operator’s hands are required to be at a safe location (on control buttons) and at a safe distance from the danger area while the machine completes its closing cycle. Two-hand trip The two-hand trip requires concurrent application of both the operator’s control buttons to activate the machine cycle, after which the hands are free. This device is usually used with machines equipped with full-revolution clutches. The trips must be placed far enough from the point of operation to make it impossible for the operator to move his or her hands from the trip buttons or handles into the point of operation before the first half of the cycle is completed. The distance from the trip button depends upon the speed of the cycle and the band speed constant. Thus the operator’s hands are kept far enough away to prevent them from being placed in the danger area prior to the slide/ram or blade reaching the full “down” position. To be effective, both two-hand controls and trips must be located so that the operator cannot use two hands or one hand and another part of his/her body to trip the machine. Gate The gate is a moveable barrier that protects the operator at the point of operation before the machine cycle can be started. Gates are, in many instances, designed to be operated with each machine cycle. To be effective, the gate must be interlocked so that the machine will not begin a cycle unless the gate guard is in place. It must be in the closed position before the machine can function. If the gate is not permitted to descend to the fully closed position, the press will not function. Another potential application of this type of guard is where the gate is a component of a perimeter safeguarding system.Here the gate may provide protection not only to the operator but to pedestrian traffic as well. FSM |
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